The present invention relates to washing machines wherein a clutch spring is employed for engagement and disengagement between a drive shaft rotated by an electric motor and a tub shaft for rotating a rotating tub.
In automatic washing machines, generally, an agitator provided in a rotating tub is forward and reverse rotated in each of wash and rinse steps and the rotating tub and agitator are rotated in one direction in a dehydration step. Since a single electric motor is provided in such a washing machine, the same is provided with a clutch for controlling transmission of the motor torque and a brake mechanism for restraining the free rotation of the rotating tub in the wash step, and the like.
FIGS. 7 and 8 illustrate one of the above-described type automatic washing machines. Referring to FIG. 7, a water receiving tub 1 is resiliently suspended in a cabinet 2. A rotating tub 3 is provided in the water receiving tub 1 and an agitator 4 is provided in the rotating tub 3. An electric motor 5 is mounted on the underside of the water receiving tub 1. A drive control mechanism 6 is also provided on the underside of the water receiving tub 1. The drive control mechanism 6 comprises a clutch and a brake mechanism. Referring now to FIG. 8 schematically illustrating the drive control mechanism 6, a drive shaft 7 is integral with a pulley 8. Rotational force of the motor 5 is transmitted to the drive shaft 7 through a transmission mechanism 11 comprising a pulley 9 secured to a rotational shaft 5a of the motor 5 and a belt 10 provided between the pulleys 8 and 9, as shown in FIG. 7. The drive shaft 7 is disposed so that a hollow cylindrical tub shaft 12 is adjacent to the upper end of the drive shaft 7 in coaxial relation. A hollow follower shaft 13 is integral with the tub shaft 12 and the diameter of the coupling portion of each of the follower shaft 13 and the tub shaft 12 is rendered larger, thereby constituting a gear case 14. The follower shaft 13 is directly coupled to the rotating tub 3. Accordingly, the tub shaft 12 is coupled to the rotating tub 3. Upon rotation of the tub shaft 12, the gear case 14, follower shaft 13 and rotating tub 3 are rotated with the tub shaft 12. An agitator shaft 15 is inserted in the hollow interior of the tub shaft 12 and directly coupled to the drive shaft 7. The agitator shaft 15 serves as an input shaft of a reduction gear mechanism 16 provided in the gear case 14. A follower shaft 17 serving as an output shaft of the reduction gear mechanism 16 is projected into the rotating tub 3 through the hollow interior of the follower shaft 13. The agitator 4 is coupled to the projected end of the follower shaft 17 and accordingly, rotated by the agitator shaft 15. The gear case 14 also serves as a brake drum of a brake mechanism 18. A brake band 20 to which a brake shoe 19 is secured is mounted on the outer periphery of the gear case 14.
A coiled clutch spring 21 is disposed about portions of the outer peripheral surfaces of the drive and tub shafts 7 and 12. The clutch spring 21 is tightly wound up about the tub shaft 12. Upon rotation of the drive shaft 7, the clutch spring 21 is adapted to be wound up to thereby transmit rotation of the drive shaft 7 to the tub shaft 12. The clutch spring 21 is formed so that the portion 21a thereof wound up at the tub shaft side has a diameter smaller than the portion 21b thereof wound at the drive shaft side, in the free state, as shown in FIG. 9. Consequently, in the state that the clutch spring 21 is disposed about the outer peripheral surfaces of the drive and tub shafts 7 and 12, the degree of winding of the portion 21a at the tub shaft side is higher than that of the portion 21b at the drive shaft side. The reason for this is that the transverse length of the portion 21a of the clutch spring 21 is reduced by increasing the degree of winding of the portion 21a, thereby reducing the axial length of the clutch spring 21. One end 21c of the clutch spring 21 (drive shaft side) is engaged with a sleeve 22 having a large number of engagement claws 22a on the entire outer periphery, as shown in FIG. 8. A clutch lever 23 is disposed so as to disengageably engage any one of the engagement claws 22a of the sleeve 22. More specifically, the clutch lever 23 engages any one of the engagement claws 22a whatever angular position the clutch spring 21 occupies. Therefore, whatever angular position the clutch spring 21 occupies, the end 21c thereof is fixed at the angular position when the clutch lever 23 engages any one of the engagement claws 22a of the sleeve 22.
In the dehydration step, the braking of the brake mechanism 18 against the tub shaft 12 is released and the end 21c of the clutch spring 21 is released by disengaging the clutch lever 23 from the sleeve 32. In this state, the drive shaft 7 is rotated by way of the motor 5 in the direction of arrow D shown in FIGS. 8 and 10. Since rotation of the drive shaft 7 in the direction of arrow D causes the clutch spring 21 to be wound up, the portion 21b of the clutch spring 21 is wound up about the drive shaft 7 upon rotation of the drive shaft 7 in the direction of arrow D, and the portion 21a of the clutch spring 21 is wound up about the tub shaft 12. Consequently, rotation of the drive shaft 7 is transmitted to the tub shaft 12, that is, the tub shaft 12 is coupled to the drive shaft 7 to be rotated therewith. In such a case, since the agitator shaft 15 is coupled with the drive shaft 7, the tub and agitator shafts 12 and 15 are rotated with the drive shaft 7, resulting in the simultaneous rotation of the rotating tub 3 and agitator 4.
In the wash or rinse step, the tub shaft 12 is braked by the brake mechanism 18 and the end 21c of the clutch spring 21 is fixed by engaging the clutch lever 23 with the sleeve 22. In this state, the motor 5 is forward and reverse rotated alternately, resulting in the alternate forward and reverse rotation of the drive shaft 7 and agitator shaft 15 in the directions of arrow D (direction of dehydration) and arrow E (see FIG. 10). Since the end 21c of the clutch spring 21 is fixed and the portion 21b has been loosened against the drive shaft 7, the clutch spring 21 is not wound up about the drive shaft 7. Consequently, the forward and reverse rotation of the drive shaft 7 is not transmitted to the tub shaft 12, and only the agitator shaft 15 integral with the drive shaft 7 is forward and reverse rotated. The rotational speed of the agitator shaft 15 is reduced by the reduction gear mechanism 16 and transmitted to the agitator 4 via the follower shaft 17, thereby forward and reverse rotating the agitator 4.
The brake mechanism 18 has a band-brake construction for enhancement of noise reduction and therefore, the braking force of the brake mechanism 18 inherently acts on the gear case 14 relatively intensely in one or the dehydration direction and relatively weakly in the opposite direction. In view of such circumstances, the brake mechanism 18 is provided with a coil spring 24 for preventing the gear case 14 from being rotated in the direction opposite to that of dehydration rotation.
The above-described conventional automatic washing machine has the following problem: the agitator shaft 15 and hence, the agitator 4 is alternately forward and reverse rotated in the wash step, with the result that water streams are caused in the rotating tub 3 so as to be directed in the directions that the agitator is forward and reverse rotated. Consequently, a load of clothes is moved with the water streams in the directions of the forward and reverse rotations of the agitator 4. In such a washing operation, the water streams and the movement of the clothes load cause the rotating tub 3 to undergo external forces acting in the directions of arrows A and B in FIG. 10, which forces cause the rotating tub 3 to rotatively move in the directions. In such a case, the tub shaft 12 is prevented from being rotatively moved in the direction of arrow B by the coil spring 24. However, since the tub shaft 12 depends upon the braking of the brake mechanism 18 with respect to the rotative movement thereof in the direction of arrow A, the tub shaft 12 is often rotatively moved in the direction of arrow A against the braking force of the brake mechanism 18 when the external force acting in the direction of arrow A is relatively large. The portion 21a of the clutch spring 21 as well as the tub shaft 12 is rotatively moved in the direction of arrow A, that is, in the direction that the clutch spring 21 is loosened. Since the end 21c of the clutch spring 21 is fixed, a torsional spring force acting in the return direction, that is, in the direction of arrow B, is accumulated in the clutch spring 21 with the rotative movement thereof. As shown in FIG. 11, when the clutch spring 21 is loosened such that a looseness angle T is reached, the torsional spring force accumulated in the clutch spring 21 overcomes the winding force against the tub shaft 12, with the result that the other end 21d of the clutch spring 21 is slipped back in the direction of arrow B and stopped at a position.
In FIGS. 10-12, reference symbol P1 indicates the position where the other end 21d (side of the portion 21a) starts rotating in the direction of arrow A, reference symbol P1' the angular position of the end 21d immediately before it is slipped, and reference symbol P1" the position where the end 21d is stopped after occurrence of slip. Further, reference symbol P0 indicates a slip limit position. When the end 21d of the clutch spring 21 is loosened in the direction of arrow A beyond an allowed looseness angle Tk in FIG. 11 in the state that the other end 21c of the clutch spring 21 is held at the angular position Pb in FIG. 10, the spring force accumulated in the clutch spring 21 is increased. Subsequently, in slipping back in the direction of arrow B, the end 21d of the clutch spring 21 reaches the slip limit position P0, with the result that the clutch spring 21 loses its looseness as a whole. In such a state, when the rotational force acts on the tub shaft 12 in the direction of arrow B or when the rotational force acts on the drive shaft 7 in the direction of arrow A, shafts 7 and 12 are immediately coupled to be simultaneously rotated. An initial looseness angle .alpha. (see FIG. 11) from the position P1 to P0 is previously determined to take the value of 5 degrees.
As obvious from the foregoing, in the case where the tub shaft 12 is rotatively moved in the direction of arrow A with the portion 21a of the clutch spring 21 in the wash step such that the clutch spring 21 is loosened, the portion 21d of the clutch spring 21 is slipped back nearly to the return limit position P0 when the looseness angle of the clutch spring 21 exceeds the allowed looseness angle Tk, with the result that the clutch spring 21 loses its looseness. Consequently, when the drive shaft 7 is reverse rotated in the direction of arrow E, the clutch spring 21 is loosened and the agitator shaft 15 is rotated without hindrance. However, when the drive shaft 7 is again rotated in the direction of arrow D, the drive shaft 7 and tub shaft 12 are immediately coupled since the initial looseness angle .alpha. has already been exceeded, resulting in the locking of the drive shaft 7 and hence, the agitator shaft 15. Consequently, the agitator 4 is not allowed to be rotated in the direction of arrow A though allowed in the direction of arrow B.